1. Field of the Invention
This invention relates to a carburetor for the internal combustion engine of an automotive vehicle, which enables the engine operating noise to be reduced when the vehicle is rapidly accelerated with a low-speed gear engaged in the automobile's transmission.
2. Description of the Prior Art
In a conventional carburetor for an automotive internal combustion engine consisting of primary and secondary barrels, the secondary barrel comes into operation when the engine is required to produce high power, whereas the primary barrel alone supplies the airfuel mixture at all other times. The secondary throttle valve is driven by an actuator responsive to the resultant of the primary and secondary venturi vacuums. The secondary throttle valve is designed to open wider as the primary venturi vacuum becomes greater.
Thus, with a low-speed gear being engaged in the automobile's transmission, when the primary throttle valve is opened wide, the secondary throttle valve is usually opened almost simultaneously, because the low-speed gear permits the engine speed to increase rapidly. However, the higher the engine speed, the louder the engine operating noise.
When the automobile is driven at high speed with the engine developing high power, the engine operating noise is not a main component of the total automobile noise, since noise caused by automobile body vibration from contact with the road surface and by passing through the air is great relative to the engine operating noise. However when the automobile is driven at a low speed with the engine developing high power, for example under rapid acceleration or when climbing a slope, the engine operating noise is a main component of the total automobile noise, since the other noise is small relative to the engine operating noise.
When the automobile equipped with such a conventional carburetor is accelerated hard with a low-speed gear being engaged, the engine operating noise forms, for instance, 50 to 70 percent of the total automobile noise.